This invention concerns a full extension locking device for a damper, especially a stay damper for closing and opening the rear hatch or trunk lid of a car, which securely maintains the fully extended state of the damper and contracts the damper when an external force is added.
Usually in a car with a rear hatch, the stay damper using a gas spring is installed between the car body and the rear hatch, and when the hatch is opened, the gas spring is extended by its gas pressure to support the weight thereof and to maintain the open state. That is, in the conventional stay damper the bearing power when the hatch is opened with the use of the repulsive power, is provided by the gas pressure only. If, however, wind pressure is applied to this hatch when the hatch is opened or if something hits the stay damper when goods are loaded or unloaded or other work is in progress at the back of the car, the gas sealing effect in the stay damper can be suddenly lost resulting in gas leakage and there is a danger of part of human body being hit by the hatch which drops with its own weight. Or if the gas is lost due to the deterioration of the seal after prolonged use, and when the hatch is opened and carelessly left, it may drop on your hand or other part of your body.
To prevent this kind of danger, several locking devices have been developed which lock the stay damper at its full extension when the rear hatch of the car is opened.
For example, there is the gas spring disclosed in the U.S. Pat. No. 3,883,126 which has a mechanical locking device that operates automatically and prevents a relative contracting movement between the piston rod and the cylinder when the gas spring approaches its fully extended position. This locking device can be manually released, but there is a danger of fingers being caught when it is released.
Another gas spring disclosed in the U.S. Pat. No. 3,938,793 has a locking mechanism consisting of a fixing element provided on the piston rod and a fixing mechanism inside the cylinder which produces resisting force together with the fixing element, but since this locking mechanism is provided inside the stay damper, it is difficult to see externally whether the lock is working or not, and if the lock is not working, there is still a danger of the rear hatch dropping.
Furthermore, the stay damper disclosed in the Japanese Pat. No. 14636/1981 has a cover, formed to surround the piston rod and fixed to the piston rod, which is automatically deformed by deforming means and blocked by the upper end of the cylinder when the stay damper is fully extended. But in this stay damper, the structure of the deforming means and the cover installing section is so complicated that its manufacture is difficult and costly.